Chem. 253 – 1/28 Lecture
Introduction
- Instructors: Roy Dixon
• Educational Background in Environmental Analytical
Chemistry
• My research in environmental chemistry has been in
the following areas:
• Cloud and Precipitation Chemistry
• Measurement of constituents of cloud droplets, rain and
snow
• Effects of snow formation type on chemical composition
• Aerosol Composition and Tracer Measurement
• Bio- and Synthetic Fuel Testing
Introduction
•
•
Undergrad at UC-San Diego (B.S.,
Environmental Chemistry)
Ph.D. in Analytical Chemistry at University
of Washington
– Thesis: Quantification of low level organic
tracer of diesel exhaust in atmospheric
particulate by HPLC-MS/MS
•
Postdoc 1: University of Wisconsin
– Projects: Source apportionment of
atmospheric particulate in Asia, Europe,
HPLC-ICP-MS for chlorinated Pt species
•
Postdoc 2: UW-Tacoma/Center for Urban
Waters
– Projects: HPLC-MS/MS for
pharmaceuticals+personal care products in
water as tracers of water quality, also PAHs in
air
•
At Sac State, continue quantifying water
quality tracers, moving into agricultural
runoff and stormwater tracers
Introduction
- Students
• Introduce yourself (name/degree plan)
• Is there anything specific you expect to
get out of the class?
Syllabus – Instructors
• I will be teaching the first third
(atmospheric chemistry) and last third
(various topics) and Dr. Miller-Schulze will
be covering the middle third (water
chemistry and various compound classes)
• I will maintain a website through my
individual website/Dr. Miller-Schulze will
use Blackboard
Syllabus – Meeting/Exams
• In graduate classes, I will typically have a 10
minute break in the middle of the lecture (with
class ending at 8:10 instead)
• This may be skipped due to class assignment in
middle of class period
• Exams: 3 exams (one on each third – no
cumulative exam; exam 3 is on day of final but
will be as long as exams 1 and 2)
• Exams will involve qualitative and quantitative
knowledge
Syllabus – Text/Exams/Reading
• Because of the single 2.5 block of time, we will
try to have group activities in the middle of the
lecture
• Exams: 3 exams (one 1 hour on each third – no
cumulative exam; exam 3 is on day of final)
• Exams will involve qualitative and quantitative
knowledge
• Most of the information will come from the Baird
and Cann text (with some supplementary
readings made available)
Syllabus
- Course Overview
• The course is partially broken up by “spheres”
–
–
–
–
–
Atmosphere
Hydrosphere
Lithosphere
Others: Biosphere
We study chemistry in each regime
• Environmental Chemists can also study:
– Natural (unperturbed) Systems
– Cause and Effect of Perturbations (e.g. pollution)
– Ways to Mitigate or Adapt to Perturbation
Syllabus
- Notes on Grading I
• Exams: 84% of total (28% each)
• Homework (8% of total)
– Mostly assigned from book
– Some problems (e.g. review questions) are
not graded
– Will randomly select one or two problems for
grading – must show work, not just answer
Syllabus
- Notes on Grading II
• In Class Group Assignments (8% of grade)
- Goal is to increase in-class participation, break
up a long lecture, and encourage learning by
doing
- Expect to have groups of 3 (could depend on
class size), assigned by instructor, with different
tasks assigned to each participant
- Will work on problems, and then turn in results
- New activity for me
- Will start with an ungraded activity today
Syllabus
- Notes on Grading III
• Group Assignments (cont.)
• This is how the active learning exercises will work
logistically:
– There will be a class list available that gives the groups and roles
for each worksheet
– You’ll sit with your group (by number) and work on an Activity
• Groups will be of 3 (and some 2’s or 4’s depending on
attendance, # of students in class)
– One person in the group will be “the calculator”, one person will
be “the recorder”, one person will be “the manager”
Syllabus
- Notes on Grading IV
• Group Assignments (cont.)
• Role Descriptions:
– Calculator (C): This is the person who operates the calculator
and performs all calculations
– Recorder (R): This is the only person who can write answers on
the worksheet to be turned in at the end
– Manager (M): This is the person who manages the group. This is
the only person who can ask me questions during the “active
learning” time
Typical Lectures
(My part)
• Mostly by powerpoint (with some example
calculations)
• Announcements in beginning
• Powerpoint slides will be made available on
website
• Group activities will be in the middle (~30 min)
• No break planned, but I could have a break
before or following the group activity
Homework Set 1
• To do before 1st Exam.
• Working on entire set, but
• Set 1.1: Ch. 1
•
•
•
•
Problems: 2, 4, 5
Review Questions: 1, 3-10
Additional Problems: 1, 5
bold problems to be turned in next lecture
• Problems to be turned in should be
worked on independently.
Today’s Topics
•
•
•
•
Biogeochemical Cycles
Introduction to Atmospheric Chemistry
The Stratosphere
Stratospheric Chemistry
Biogeochemical Cycles
• Mostly not covered in text
• What is a Biogeochemical Cycle?
– If we can define different regions as “spheres”,
we can define biogeochemical cycles as the set
of spheres and the flow paths in and between
different spheres
• Why am I covering them?
– They are very useful for putting problems in
perspective
– Examples:
• anthropogenic vs. natural sources
• reservoir vs. flux species
Biogeochemical Cycles
• Familiar Example (that is in text)
Water Cycle – a largely non-chemical transformation cycle
Green Numbers are
Amounts
(Reservoirs)
Black Numbers are
Fluxes (transport
from one to
another reservoir)
Baird and Cann, p. 410
Biogeochemical Cycles
• Can also use box and arrow approach
• “Box models” are among the simplest
models describing cycling
atmosphere
Ice
oceans
Note: atmosphere is nearly
insignificant as reservoir, but very
important for fluxes
Biogeochemical Cycles
• Another Example: Sulfur Cycle
Pollution (e.g. burning
S-containing coal)
significantly affects
continental atmosphere
Although Sulfate is a
major constituent of
sea water, marine biota
emissions ((CH3)2S) is
a significant source of
atmospheric S
Butcher et al., Global Biogeochemical Cycles
Biogeochemical Cycles
• Carbon Cycle – small fluxes (Fossil Fuel C)
can put reservoirs out of balance due to
“quick cycling” (in surface ocean and biota)
Butcher et al., Global Biogeochemical Cycles
Biogeochemical Cycles
• Cycles covered are very general and don’t
cover a variety of pathways within boxes
• Additionally most spheres or boxes need to
be subdivided due to differences in
pathways
Butcher et al., Global
Biogeochemical
Cycles
Biogeochemical Cycles
• Simple Modeling Math
– For a reservoir (mass M) with one source (Q)
and one sink (S), at steady state:
Reservoir
dM/dt = Q - S
S (flux out)
– turnover time = t = M/S (how long it would
take the reservoir to empty if the Q =0)
Q (source)
– A common sink is proportional to
concentration (or reservoir mass, M): S = kM
and t = M/S = 1/k
– With S proportional to M, exponential decay
is expected and t is also the “e-folding time”
Introduction to Atmospheric
Chemistry
• Atmospheric Composition
– 78% nitrogen (N2) – pretty inert
– 21% oxygen (O2) – fairly inert in lower atmosphere
– ~1% Ar
• Concentration units (for non-major species)
– parts per million by volume (ppmv)
= (nX/nair)·106 (where n = moles)
– partial pressures (atm, e.g. for Henry’s law
calculations)
– concentrations (molecules/cm3 for kinetic
calculations)
– A well mixed gas (e.g. Ar) will have constant mixing
ratio with altitude but a decreasing concentration
Introduction to Atmospheric
Chemistry
• Source of Oxygen
– Not a stable gas (metals, carbon like to be
oxidized)
– Produced by biota (and then changed the
atmosphere)
• Structure of Atmosphere
– Pressure decreases with height (as with other
fluids)
– If the atmosphere is considered isothermal (it
isn’t), P = Poe-Z/H (where P = pressure, Po = 1
atm, Z = height, and H ~ 8 km)
Introduction to Atmospheric
Chemistry
• Structure of Atmosphere – cont.
– The main gases are invisible to the
light reaching the lower
atmosphere
– Little direct solar heating occurs in
the lower atmosphere
– Surface heating from sunlight
creates less dense air (n/V =
P/RT), which rises and cools
adiabatically
– This results in a general decrease
in T with increase in Z (height
above sea level).
Z (km)
T (°C)
Introduction to Atmospheric
Chemistry
• Structure of Atmosphere – cont.
– Exceptions to profile
Z (km)
• near ground at night (radiation cools
surface faster than surrounding air –
why we can have frost at T > 0°C)
• In stratosphere (to be explained in
more detail)
T (°C)
Introduction to Atmospheric
Chemistry
• Atmospheric Layers
– highest layers (not covered here)
– stratosphere (~12 to 48 km)
– troposphere (0 to ~12 km)
• Stratosphere occurs due to change in
lapse rate due to atmospheric heating
from absorption of solar light
• Warmer stratosphere makes mixing with
lower atmosphere very slow (hard to get
cold tropospheric air to rise into warmer
stratosphere)
Stratospheric Chemistry
short UV
• The sun emits a full range of
light
• Short UV light is absorbed by
nearly all gases
• O2 absorbs light under ~220 nm
• This generates heat (and the
reversing of the lapse rate)
• some absorption results in
photolysis:
O2 + hn → 2O
Z (km)
visible light
Stratospheric Chemistry
• Prediction of efficacy of light for
photolyzing bonds:
– can compare Ephoton with Ebond
– when Ephoton > Ebond, photolysis is possible
– Ephoton = hc/l (note: calculated per
molecule while E is given per mole)
Stratospheric Chemistry
• Ozone Formation Reaction:
O + O2 + M → O3 + M
- M is needed to remove excess energy (can
write in more detail as:
O + O2 → O3*
and O3* + M → O3 + M + heat, where
O3* refers to an excited state of O3)
• Ozone is generated where O can form
(also is generated through separate
tropospheric chemistry reactions)
Stratospheric Chemistry
• Value of Ozone in the Stratosphere
– Ozone has weaker bonds than O2 and
absorbs longer wavelength UV light
– Absorbs light effectively in the 220 to 290
nm range
– This protects life in the lower atmosphere
• Full Set of O only reactions
O3 + hn → O2* + O*
and O3 + O → 2O2 (odd O ending rxn)